Many of us have witnessed sun pillars--columns of light that lance upwards from the horizon just as the sun is rising or setting. They are caused by plate-shaped ice crystals in clouds that bend the rays of the low-hanging sun. While sun pillars are frequently seen, in all seasons and at all latitudes, elusive companions of sun pillars may have been frequently overlooked. They are called sun pillar "echos":

Atmospheric optics expert Les Cowley explains: "13 years ago in Finland, three halo experts saw peculiar 'echoes' straddling an otherwise ordinary sun pillar. They could not be explained and there the matter rested for want of confirmation by another observation. Then, last week, Jon Inghram sent me several sun pillar images. He too had noticed faint 'echoes' on each side of his pillar – the mysterious ice halo was at last confirmed!" "More details and pictures may be found in an article here. But we still cannot explain them. The Finland observers, Jon and I have each tried simulations using the flattened pyramid crystals invoked to account for elliptical halos. They do not work at all well. We need many more observations! Take plenty of pictures of each pillar. The echoes are easily overlooked or mistaken for cloud patches and have probably been seen many times. Observations under different conditions could help unravel their mystery." http://spaceweather.com/